Why does my string trimmer line not come out when I bump it?

The head may not be a bump-feed design, or the spool may be wound incorrectly, jammed, empty, or loaded with the wrong line diameter. Check the head instructions, then inspect the spool, eyelets, bump knob, and spring with the power disconnected.

How long should trimmer line be after bumping?

The correct length depends on the head design. It should extend evenly from both outlets and remain within the length specified by the trimmer or head manufacturer. Do not keep bumping if the line remains unusually short.

Can I use a thicker line to make it last longer?

Only if the trimmer head and motor are rated for that diameter. Thicker line can bind in the spool, overload the motor, reduce cutting performance, and prevent bump feeding.

Should I replace the whole trimmer head?

Replace the head when the bump knob, housing, spool supports, spring, or line outlets are damaged and the affected parts are not available separately. Make sure the replacement matches the trimmer's mounting system and operating requirements.

If the line is too short after a bump, the head may be empty, wound incorrectly, clogged, damaged, or not designed to feed by bumping. Follow these checks before replacing the trimmer.

Line too short after a bump

If your string trimmer line stays too short after you bump the head, the most likely causes are an empty or incorrectly wound spool, a jammed feed path, a damaged bump head, or a trimmer head that does not use bump-feed operation. Turn the trimmer off, disconnect the battery or spark plug when applicable, and inspect the head before trying to feed more line.

Check whether the head is supposed to bump-feed

Not every trimmer head releases line when tapped on the ground. Some use:

Manual line-feed buttons
Fixed-length pieces of line
Automatic feed mechanisms
A bump knob that must be pressed while the head is rotating

Check the trimmer and head instructions first. If the head is a fixed-line design, bumping it will not extend the line. If it is an automatic-feed head, bumping may also be unnecessary or incorrect.

Inspect the spool and remaining line

Remove the head cover according to the manufacturer's instructions. Look for these common problems:

There is too little line on the spool. The ends may be too short to reach the outlet openings. Refill the spool with the correct diameter and type of trimmer line.
The line has slipped under another wrap. Crossed or loose wraps can prevent the spool from releasing line.
The line is wound in the wrong direction. Most spools have an arrow showing the winding direction. Reverse winding can stop bump feeding.
The line is fused together. Heat from friction can melt adjacent wraps into a solid mass, especially with some nylon lines. Remove the damaged line and rewind fresh line.
The wrong line diameter is installed. Oversized line may bind in the eyelets or spool, while undersized line may feed unpredictably.

Do not force a spool that does not fit easily. A replacement spool should match the trimmer head and the line diameter specified by the manufacturer.

Clear the eyelets and feed path

Grass, dirt, and melted line can block the small openings where the line exits the head. With the power disconnected, pull out loose debris and check that both eyelets are open.

If the line is stuck inside an eyelet, do not probe aggressively with a sharp tool that could damage the opening. Remove the spool and clear the obstruction using a blunt plastic tool or replace the eyelet or spool if it is deformed.

Also check whether the line ends are different lengths. Uneven ends can make the head vibrate and may stop the shorter end from feeding normally.

Check the bump knob and head for damage

A bump-feed head relies on the bump knob, spool, spring, and internal indexing parts moving freely. Look for:

A bump knob that is cracked or worn flat
A spool that will not rotate inside the housing
A missing or collapsed spring
Broken tabs on the spool or cover
A head that is packed with grass or dirt
Excessive wear around the line outlets

The bump knob should move or rotate as described in the instructions, without binding. Do not operate the trimmer with a cracked head, missing cover, loose eyelet, or damaged retaining hardware. Replace the affected head or part rather than trying to repair a rotating component with improvised fasteners.

Use the correct bumping technique

Once the head is correctly loaded, hold the trimmer in its normal cutting position and run it at the operating speed recommended in the manual. If the design calls for bump feeding, briefly tap the bump knob against a firm, suitable surface while the head is rotating. Do not strike the head hard or repeatedly against concrete, rocks, or metal; that can damage the knob and housing.

If one light bump releases line but the line remains very short, stop and inspect the spool again. Repeatedly bumping a malfunctioning head is unlikely to fix a jam.

Check for incorrect setup or a full line head

Some replacement heads use a different loading method from the original head. Confirm that:

The spool is seated in the correct orientation
The line passes through both eyelets before the cover is installed
The cover is fully locked but not distorted
The retaining nut, bolt, or adapter is installed in the correct order
The line length and diameter match the head's instructions

A spool that is overfilled can bind just as readily as an empty one. Leave the clearance specified by the head manufacturer rather than packing on as much line as possible.

When to replace the line, spool, or head

Replace the line when it is brittle, fused, badly kinked, or the wrong diameter. Replace the spool when its tabs, eyelets, or winding surfaces are damaged. Replacing the complete head is reasonable when the bump knob, housing, spring, or internal feed mechanism is worn and individual parts are unavailable.

Choose a replacement head only if its mounting hardware, rotation direction, line diameter, and guard arrangement are compatible with your trimmer. A head that does not fit securely can create a serious thrown-object hazard.

If a correctly loaded spool still will not feed, and the head is damaged or the drive area wobbles, stop using the trimmer. For gasoline models, persistent feed problems accompanied by unusual vibration should be inspected with the engine off by a qualified repair professional or addressed using the manufacturer's service guidance.